1. Field of the Invention
The present invention relates to an etching apparatus for semiconductor substrates (also called wafers) and, more particularly, to an etching apparatus for etching the end surfaces of semiconductor substrates.
2. Description of the Related Art
In the manufacture of semiconductor devices, an etching process is sometimes performed for only the end surface surface of a semiconductor substrate. For example, a disk-like wafer having no orientation flat is used as a semiconductor substrate for a large-power semiconductor device or the like, and the side surface of the wafer is inclined with respect to the major surfaces of the wafer so as to form a bevel structure to maintain a prescribed breakdown voltage. Since cracks and defects are produced on the inclined side surface of the wafer during beveling, they must be removed by etching. Such a conventional technique for etching only the end surface of a wafer will be described with reference to the accompanying drawings.
As shown in FIG. 1A, after one major surface of a wafer 1 is entirely coated with an antietching solution 2 using a brush, the wafer 1 is bonded to a fluoroplastic disk 3 having the same diameter as that of the wafer 1. The wafer 1 and the disk 3 are then placed on a hot plate with the disk 3 facing down, and are baked for several minutes to be fixed on each other. After baking, the other major surface (pattern formation surface) of the wafer 1 is coated with the antietching solution 2 using a brush. The wafer 1 is then baked in the same manner as described above. In the above-described process, it is essential to prevent adhesion of the antietching solution to the end surface of the wafer 1.
As shown in FIG. 1B, the above-described wafer with the fluoroplastic disk is picked up with tweezers 4 and is immersed in an etching solution 6 in an etching solution tank 5 for a predetermined period of time, thus etching only the end surface of the wafer. After etching, the etching solution is completely removed from the wafer with the disk by cleaning with water. In addition, the wafer is immersed in a boiling organic solution so as to peel off the disk 3 from the wafer 1 and to remove the antietching solution. Upon removal of the antietching solution, the wafer is picked up with the tweezers and is swung in a water flow tank to clean it. After cleaning, as shown in FIG. 1C, the wafer is placed below an ultraviolet lamp 7 to dry it.
The following problems are posed in the above-described conventional etching means. (1) An anti-etching solution must be carefully coated on the major surfaces of a wafer so as to prevent the solution from adhering to the end surface of the wafer. Hence, the coating step requires a long period of time. (2) It takes an undesirably long period of time to bond a fluoroplastic disk to the wafer while preventing adhesion of the antietching solution to the end surface of the wafer. (3) In order to remove the hardened antietching solution after the wafer is immersed in the etching solution, the cumbersome subsequent steps are required: immersing the wafer in a boiling organic solution; cleaning in flowing water; and drying by means of a lamp. (4) After the fluoroplastic substrate is peeled off from the wafer, the wafer is picked up with tweezers so as to be set or reset in a drying process by means of a lamp. For this reason, the end surfaces of wafers tend to break (chip), resulting in a decrease in yield. (5) Since the coating film of an antietching solution on both the major surfaces of a wafer varies in thickness, the manufacturing yield is decreased. (6) Since an operator is required to perform a large number of steps, such as coating an antietching solution, bonding a fluoroplastic disk, peeling the antietching solution and the disk, and drying by means of a lamp, automation is delayed and a long period of time is required for these steps. (7) Large amounts of etching solution and organic solution are used. (8) Since harmful solutions are used, pollution problems are posed. (9) The delivery date of products is difficult to keep because of a large number of steps.
As described above, in the conventional technique, the number of steps to be performed by an operator is large, and it is difficult to uniformly etch the end surface of a wafer, thus position problems in terms of quality and yield. In addition, a long period of time is required for the respective steps, such as etching, cleaning, and drying, and large amounts of etching solution, organic solution, and the like are used, thus posing a problem in terms of safety with respect to a human body.